KR101666250B1 - Single column stripping and drying process - Google Patents

Abstract

The organic material is stripped and dried in a single column with two contact zones. The stripping gas is introduced into the upper contact zone and flows through the organic material in this zone. The dry gas is introduced into the lower contact zone. The dry gas contacts the organic material at both the upper and lower contact zones and is removed at the top of the column with the stripping gas. This method requires very efficient stripping of volatile organic compounds as well as efficient drying and low levels of stripping and drying gas.

Description

[0001] SINGLE COLUMN STRIPPING AND DRYING PROCESS [0002]

This application claims priority to U.S. Provisional Patent Application No. 61 / 246,654, filed on September 29, 2009.

The present invention relates to a method of stripping impurities from organic polymers and organic polymers such as poly (alkylene oxide) polymers.

Many organic compounds and polymers are prepared using processes that leave a certain level of impurities and / or moisture thereon. It is often necessary to remove such impurities and moisture to very low levels so that the product is suitable for use in the downstream process. There are many such cases in the chemical industry. One prominent example is the preparation of poly (alkylene oxide) polymers in which the crude polyol often contains a significant amount of volatile aldehyde impurities, and impurities, among other things, impart a toxic odor to products such as polyol and polyurethane foams produced therefrom do. In addition, polyether polyols often contain up to 5% by weight of water, which can be used in polyurethane manufacturing only after they are reduced to a much lower level. A related manufacturing process is the production of so-called polymer polyols by polymerization of monomers such as styrene and / or acrylonitrile in the presence of poly (alkylene oxide) polyols. The polymer polyol product generally contains significant amounts of volatile organic impurities, particularly unreacted monomers, which can be used after the product has been removed from the product.

The stripping method is commonly used to remove volatile impurities from organic compounds to very low levels. One common approach to stripping is to pass the organic compound downward to the stripping column, often at subatmospheric pressure. The stripping gas, usually steam, is countercurrent to the organic compound and passes upward through the column to transport volatile organic impurities out of the top of the column.

Stripping processes for removal of volatile impurities from polyether polyols are described, for example, in USP 6,060,627 and US Published Patent Application Nos. 2008/0033139 and 2008/0033214. In USP 6,060,627, propoxylated glycerin containing water, allyl alcohol and propylene glycol allyl ether is sent to a reboiler evaporator to remove a large amount of water, followed by vacuum stripping with steam as a stripping gas. The weight ratio of steam to treated polyether polyol mixture is about 0.0287: 1. US 2008/0033139 describes a two-column stripping apparatus for stripping residual monomers from a polymer polyol product. The examples of this application describe very high steam to polyol ratios (0.2: 1 weight ratio). It has been described that high levels of steam reduce levels of residual monomers and isopropanol from about 12,000 to 13,000 ppm to 1 ppm each, with more typical results ranging from 10 to 20 ppm. Also, certain impurities "recombinant products" remain in the polyol at levels of several hundred ppm, and the water content does not decrease or even increases.

US 2008/0033214 describes a stripping process of polyether polyols mentioned as having up to 100 ppm of volatile organic compounds prior to treatment. This stripping process removes it to a level of only 20 ppm, which is said to be sufficient to reduce odors, but is still significant. The weight ratio of the stripping gas to the polyol is mentioned as 0.01 to 0.05. The example describes stripping using nitrogen as a stripping agent.

Drying can also be carried out in a column, by passing the dry gas through the column with a flow of organic material into the stream.

It is desired to effectively remove the volatile organic impurities to a very low level, for example, 10 ppm or less, and to remove water to a low level, for example, 200 ppm or less, and to develop efficient and inexpensive stripping and drying methods .

The present invention is such a method. The present invention

a) introducing the starting organic material into the upper contact zone of the column having an upper contact zone and a lower contact zone and causing the starting organic material to move downward through the column through the upper contact zone and then through the lower contact zone to the bottom zone of the column ;

b) introducing the stripping gas into the upper contact zone of the column and above the lower contact zone of the column such that the stripping gas contacts the starting organic material through the upper contact zone in the upper contact zone and impurities therefrom Removing it and then moving it upward to the top zone of the column;

c) introducing a dry gas into the lower contact zone of the column such that the dry gas is moved upward through the lower contact zone, the dry gas in contact with a portion of the organic material in the lower contact zone and removing moisture therefrom, - in the upper contact zone, the drying gas is brought into contact with another part of the organic material, followed by movement to the uppermost zone of the column;

d) removing the stripping gas and the drying gas from the column top region above the upper contact zone; And

e) stripping and removing the dried organic material from the column bottom zone below the lower contact zone

≪ / RTI > and a method of stripping and drying the starting organic material.

The stripping method of the present invention provides several potential advantages over the conventional approach of separately performing the stripping and drying steps. Equipment costs are lower because stripping and drying are performed in a single column instead of multiple columns. Volatile organic impurities can often be reduced to very low levels using surprisingly small amounts of stripping gas. This reduces the material cost and reduces the cost of handling more volume of gas. When the stripping gas is steam as desired, the present invention also reduces the energy cost (because less steam is needed to be produced) and the wastewater treatment cost (e.g., the removal of condensed steam and volatile organic compounds entrained therein) ≪ / RTI > The dry gas passes through the upper contact zone and contacts the organic material there, thereby contributing to the stripping taking place in the upper contact zone, thus reducing the amount of stripping gas required. This reduces the size and cost of the vacuum system which must operate the column at reduced pressure.

This method is well suited to continuous processes, which likewise reduces costs and in some cases eliminates the need for organic material storage prior to stripping and drying processes. Removing or reducing material storage may in some cases reduce or eliminate the need to add a stabilizer such as an antioxidant, adjust the pH of the material, or perform other pretreatments on the material, as in the case where the organic material is a polyether.

The figures are schematic diagrams of the method of the present invention.

Referring to the drawings, the stripping column 9 comprises a liquid inlet 1 through which a starting organic polymer or compound containing volatile organic impurities is introduced into the column 9. [ The starting organic material flows downward through the upper contact zone 2 of the column 9 after entry into the column 9. The stripping gas is introduced into the upper contact zone 2 of the column 9 through the stripping gas inlet 5. The stripping gas inlet 5 is below the liquid inlet 1 and above the lower contact zone 3 where the starting organic material is introduced into the column. In general, the location of the stripping gas inlet 5 will delimit the boundary between the upper contact zone 2 and the lower contact zone 3 of the column 9.

The stripping gas introduced into the column 9 through the gas inlet 5 moves upward through the upper contact zone 2 to contact the starting organic compound or polymer and to remove impurities (relative to the organic material) At least partially stripping. The stripping gas with accompanying impurities is then moved upwardly to the top zone 10 of the column 9 and exits the column 9 through the gas outlet 4. The uppermost zone 10 is generally the portion above the liquid inlet 1 of the column 9 where the gas can accumulate and be removed from the column 9 through the gas outlet 4.

The organic material moved down through the upper contact zone 2 then flows into the lower contact zone 3 of the column 9. The dry gas is introduced into the lower contact zone 3 through the drying gas inlet 6 to contact the organic material and remove moisture therefrom. In general, the position of the dry gas inlet 6 will define the boundary between the lower contact zone 3 and the bottom zone 8 of the column 9. [ The dried organic material then flows to the bottom zone 8 of the column 9 and collects below the drying gas inlet 6 and is removed therefrom through the outlet 7 from the column 9. After passing through the lower contact zone 3, the drying gas is moved upward through the column 9 to the upper contact zone 2, so that at the same time the organic material is in contact with the stripping gas, Contact. It is believed that the dry gas contributes to the stripping process taking place in the upper contact zone 2. The dry gas then moves to the top zone 10 and is removed with the stripping gas through the gas outlet 4.

In addition to having the specific features described above (i.e., various inlet and outlet, and upper and lower contact bands), the stripping column 9 need not have any particular structure or design. It can be composed of any suitable material in view of the operating conditions (mainly temperature and pressure), the particular organic material, the particular stripping gas and the particular dry gas. Various grades of steel or aluminum are generally suitable.

The stripping column 9 will generally contain at least an upper contact zone 2 and a lower contact zone 3. Packing more evenly distributes the organic material across the cross section of the column, increases the residence time of the organic material in the column and increases the surface area of the organic material to promote better contact with the stripping and drying gases, And to contribute to the purpose of facilitating. A wide variety of porous materials are suitable as fillers and include meshes, wool, fibers, a series of porous plates, beads or other particulates, various types of structured fillers, trays, and the like. As before, the constituent materials are not considered significant and will be selected in view of the operating conditions and the particular organic material, stripping gas and dry gas. Metal and ceramic fillers are generally preferred. If metal fillers are used, the metal must be resistant to chemical attack from water and / or other chemical species.

The stripping column 9 may contain one or more supports to hold the filler material in place in the column.

The filler in the stripping column 9 may have a specific surface area of 150 to 500 m < 2 > / m < 3 >. The preferred specific surface area is 230 to 450 m < 2 > / m < 3 >.

The stripping column 9 may have a jacket that provides temperature control by applying a heating or cooling medium, such as steam, to the outside of the column. Other heating and cooling devices may be present in addition to or instead of the jacket.

The stripping column 9 will also generally contain means for distributing the stripping gas supplied by the stripping gas inlet 5 over the entire cross section of the column. Thus, the stripping gas inlet 5 is generally in fluid communication with the stripping gas distributing means through which the stripping gas will be received from the stripping gas inlet 5 and introduced into the stripping column 9. The stripping gas distributing means preferably introduces the stripping gas into the column (9) at a plurality of locations throughout its cross section. Stripping gas distribution means may include, for example, one or more distribution plates, spargers, bubbles, jets, nozzles or similar devices.

Similarly, the dry gas inlet 6 will also generally be in fluid communication with the means for distributing the dry gas across the cross-section of the stripping column 9. [ Suitable designs for such dry gas distribution means include those mentioned above with respect to the stripping gas distribution means.

The stripping column 9 may contain means for distributing the organic material introduced through the inlet 1 to the entire cross section of the column. Likewise, specific devices such as those mentioned above with respect to the stripping gas distributing means are all suitable.

The gas outlet 4 preferably comprises gas eliminating means for evacuating stripping and drying gas from the column 9 and for applying vacuum to the column 9 when it is necessary to operate the column 9 below atmospheric pressure Fluid communication. The gas removal means may have any suitable design. Mechanical devices such as simple fans or blowers and vacuum pumps of various designs are suitable. If the stripping gas is steam or other readily condensable gas, the degassing means may comprise or consist of one or more condensers that condense some or all of the removed gas to produce a vacuum in the system. A combination of these approaches may be used.

The outlet 7 is also preferably in fluid communication with the pumping means for stripping and draining the dried organic material from the column. The pumping means is any kind of device capable of moving liquid through the conduit. Various types of pumps and impellers are suitable. The design of the pumping device is not considered significant in the present invention.

The organic material is any organic compound or mixture of organic compounds that is liquid under the conditions in which the stripping column is operating. The mixture of organic compounds may comprise a solution of one material in a solvent, in which case the solvent may be either a process solvent from any upstream stage, or it may dissolve other organic materials for processing through a stripping column, Lt; / RTI > The organic material is generally more volatile than the organic material (more volatile than any solvent needed to keep the organic material in liquid during stripping and drying processes) prior to treatment according to the present invention and can be removed by stripping Containing one or more impurities. The organic material may contain moisture, i.e., a small amount of water, before being introduced into the stripping column 9. [ This is usually the case when the stripping gas is something other than steam. When steam is used as the stripping gas, the organic material will typically absorb some moisture from the steam in the upper contact zone 2, which is then removed via contact with the drying gas in the lower contact zone 3 do.

The organic material may comprise or consist of one or more organic polymers (other than impurities and water), which may or may not be soluble in any solvent.

The starting organic material may contain, for example, from 10 to 20,000 ppm by weight of volatile organic impurities. Higher levels of organic impurities are difficult to remove at very low levels in the stripping process. The preferred level of volatile organic impurities in the starting organic material is 50 to 5,000 ppm, more preferred levels are 50 to 2,000 ppm. The starting organic material may contain up to 50,000 ppm of water, up to 10,000 ppm of water, up to 5,000 ppm of water, or up to 2,500 ppm of water.

A preferred organic material is a crude liquid polyether having a molecular weight of about 500 to 10,000, which is the product of alkylene oxide polymerization. The alkylene oxide may be, for example, ethylene oxide, propylene oxide, butylene oxide, 1,2-hexane oxide, tetrabutylene oxide, styrene oxide, or a mixture of two or more thereof. These oxides can be polymerized by an anionic polymerization process in the presence of an initiator compound and an alkali metal hydroxide catalyst. Alternatively, the oxides can likewise be polymerized in the presence of an initiator compound using a double metal cyanide catalyst complex. The crude liquid polyether will generally terminate with a hydroxyl group and may, for example, have from 1 to 12 hydroxyl groups per molecule. The crude liquid polyether prepared in this manner will typically contain a large number of organic impurities including unreacted oxides, various aldehyde byproducts, etc., which are more volatile than liquid polyethers and prone to stripping in the stripping process . Polyethers prepared using anionic polymerization processes are often further processed to neutralize and remove catalyst residues, and for this reason often contain a certain amount of entrained water.

Another preferred organic material is a crude polymeric polyol obtained from the process of polymerizing one or more ethylenically unsaturated monomers in the presence of a polyether polyol. Such crude polymeric polyol products tend to contain up to 20,000 ppm, preferably up to 10,000 ppm unreacted monomers, chain transfer agents, free radical initiators and / or decomposition residues thereof.

The stripping gas is selected to be present in the gaseous phase under the conditions used in the stripping column and not react with the organic material. The stripping gas also preferably has low solubility in the organic material. The preferred stripping gas is readily condensable, since in this case it is possible to vacuum within the stripping column by condensation of the stripping gas removed from the column. Superheated steam is a particularly desirable stripping gas. By "superheating" it is meant that steam is present at a temperature above its dew point under the operating conditions of the column. Gaseous mixtures can be used, for example superheated steam and air, or superheated steam and mixtures of inert gases such as nitrogen or argon. The amount of stripping gas may be in the range of 0.0002 to 0.1 kg or more per kg of organic material. A preferred amount is from 0.0002 to 0.03 kg per kg of organic material, more preferably from 0.0002 to 0.02 kg per kg of organic material.

The dry gas is also present in the gaseous phase under the conditions used in the stripping column and does not react with the organic material, and is preferably selected to have low solubility in the organic material. The dry gas should contain no more than 100 ppm water, preferably no more than 50 ppm water. Dry air is a useful stripping gas, but argon and especially inert gases such as nitrogen are preferred. The amount of dry gas may range from 0.0001 to 0.1 kg per kg of organic matter. The preferred amount is 0.0001 to 0.003 kg per kg of organic matter.

The temperature and pressure conditions under which the stripping and drying process is performed will, of course, vary depending on the particular organic material, the nature of the organic impurities, and the particular stripping and drying gases used. The temperature and pressure within the stripping column maintains the liquid state as the organic material passes through the column (apart from the volatile organic impurities that are to be removed), and the stripping and drying gases remain in the gaseous state as they move up through the column . Pressure below atmospheric pressure is desirable to facilitate removal of volatile organic impurities and water from the organic material. The internal pressure of the stripping column may be, for example, from 5 to 100 mbar or from 15 to 50 mbar. Suitable temperatures may be from 0 to 160 캜. The preferred temperature is 90-150 占 폚, especially when polyether is stripped, and the more preferred temperature is 120-140 占 폚.

It is generally desirable to reduce the amount of organic impurities and water in the treated organic material to very low levels, for example less than 10 ppm for organic impurities and less than 200 ppm for residual moisture. It is more preferable to reduce the level of the volatile organic impurities to 1 ppm or less.

The following examples are provided to illustrate the invention and are not intended to limit its scope. All parts and percentages are by weight unless otherwise indicated.

Example 1

A single stripping column designed as shown in Fig. 1 was constructed. A crude polyol containing 6,000 ppm of water and 1,000 ppm of volatile organic impurities was passed through the column at 130 ° C. The column was operated at 15 mbar. The stripping gas was superheated steam and the dry gas was nitrogen. Only 0.005 kg of steam per kg of crude polyol was required to reduce the amount of volatile organic impurities to 0.5 ppm. The amount of nitrogen dry gas was only 0.0004 kg per kg of crude polyol, which was sufficient to reduce the water content to 100 ppm. Thus, with the present invention, not only the steam consumption is extremely low in addition to the almost complete elimination of volatile organic compounds, but also the total amount of the stripping gas and the dry gas is very small and the water content is drastically reduced.

Claims (10)

a) introducing the starting organic material into the upper contact zone of the column having an upper contact zone and a lower contact zone, and moving the starting organic material downward through the column through the upper contact zone and then through the lower contact zone to the bottom zone of the column ;
b) introducing the stripping gas into the upper contact zone of the column and above the lower contact zone of the column such that the stripping gas contacts the starting organic material through the upper contact zone in the upper contact zone and impurities therefrom Removing it and then moving it upward to the top zone of the column;
c) introducing a dry gas into the lower contact zone of the column such that the dry gas is moved upward through the lower contact zone, the dry gas in contact with a portion of the organic material in the lower contact zone and removing moisture therefrom, - in the upper contact zone, the drying gas is brought into contact with another part of the organic material, followed by movement to the uppermost zone of the column;
d) removing the stripping gas and the drying gas from the column top region above the upper contact zone; And
e) stripping and removing the dried organic material from the column bottom zone below the lower contact zone
Lt; / RTI >
The starting organic material is a liquid polyether having a molecular weight of 500 to 10,000 or a crude polymer polyol containing 50 to 5000 ppm of volatile organic impurities and 50,000 ppm or less of water and the stripped and dried organic material has an organic volatility of 10 ppm or less A compound and up to 200 ppm water. The method of claim 1, wherein the stripping gas is superheated steam. The process according to any one of claims 1 to 5, wherein the dry gas contains not more than 50 ppm of water. The process according to any one of claims 1 to 3, wherein 0.002 to 0.03 parts by weight of stripping gas per weight of organic material is passed through the column. 5. The method of claim 4 wherein 0.0001 to 0.1 part by weight of dry gas is passed through the column per weight of organic material. 3. The method of claim 1 or 2, wherein the column is operated at a pressure of from 5 to 100 mbar. 7. The method of claim 6 wherein the column is operated at a temperature of from 90 to 150 < 0 > C. delete delete delete

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